1. Field of the Invention
This invention relates in general to antenna systems, and in particular to an antenna cluster configuration for wide-angle coverage.
2. Description of Related Art
Communications satellites have become commonplace for use in many types of communications services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, satellites must provide signals to various geographic locations on the Earth's surface. As such, typical satellites use customized antenna designs to provide signal coverage for a particular country or geographic area.
In order to provide signal coverage over a large area, several approaches are used. A single beam with a wide beamwidth is sometimes used, but is limited in terms of power delivery over such a large geographic area. Typically, to cover a large geographic area, contiguous spot beams are used.
Contiguous spot beams are generated by multiple antennas to cover a large geographic area with a small variation in measured signal strength at the ground. However, in order to generate high-performance beams over the northern and southern hemisphere with a single spacecraft, it is necessary to use either a three to four wide-scan antenna configuration, or a six narrow-scan antenna configuration.
A wide scan antenna is typically a Side Feed Offset Cassegrain (SFOC) or a lensed antenna. Currently, spot-beam satellites using Ku and Ka-band communications links require antenna apertures of 100 inches. Accommodating four one hundred inch apertures on a single spacecraft is difficult. For example, the SFOC geometries are suitable on the East and West sides of the spacecraft, but not on the nadir of the spacecraft. The alternative six narrow-scan antenna configuration also required complex mechanical packaging.
It can be seen, then, that there is a need in the art for antenna systems that can deliver contiguous spot beams over large geographic areas. It can also be seen that there is a need in the art for antenna systems that can deliver contiguous spot beam coverage over both the Northern and Southern hemispheres. It can also be seen that there is a need in the art for antenna systems that provide ease of mechanical design and construction to reduce spacecraft costs.